Silica-supported catalysts for use in the polymerization of ethylene, propylene, and the copolymerization of ethylene with 1-butene, 1-hexene, 1-octene, and other alkenes are well-known. One type of these silica-supported catalysts is Ziegler-Natta catalysts, which are comprised of reaction mixtures of transition metal compounds and organometallic compounds, primarily organometallic compounds of magnesium and aluminum. Ziegler-Natta catalysts are commonly supported on MgCl.sub.2 but silica-supported Ziegler-Natta catalysts are also known. U.S. Pat. No. 3,787,384 discloses catalyst synthesis by reaction of silica with an organomagnesium compound and subsequent treatment of the product with titanium tetrachloride. U.S. Pat. No. 4,374,753 discloses a method in which the silica support is reacted with certain organic silicon compounds to give higher activity, higher melt index capability, and narrower molecular weight distribution. U.S. Pat. No. 4,388,220 discloses a method in which the organomagnesium compound is reacted with alcohols, amines, or carboxylic acids prior to reaction with the silica support, followed by subsequent treatment with the titanium component.
A primary goal of catalyst development is to improve the catalyst activity, typically measured as the rate of polymer production per unit weight of catalyst.
The polyolefins that are made with silica-supported catalysts are suitable for many applications, including injection molding and injection blow molding of thick walled bottles and other containers, coatings for wires and cables, containers such as bags, among many other known uses.